反転視野と空間識

Spatial cognition with reversed visual input

Stratton（1897）によって初めて視野を連続的に反転させる実験が報告されて以来，視野を反転させる手法は，空間認識のメカニズムや適応可能性を調べるために用いられてきた。ここでは主として，視野の左右を反転させる場合について，初期状況と長期の順応的変化を述べる。視野の反転は通常の視覚と運動の協応関係を無効にし，動作の困難のみならず，空間視の崩壊を引き起こす。空間視の崩壊は，視覚と触覚の乖離，空間定位の喪失，自己身体の分裂，視野動揺，両眼立体視の奥行反転などの様相を示す。反転メガネ着用を続けると，これらの異常な知覚現象は解消の方向へと向かう。しかし，それは写真のネガを反転させるような単純かつ全体的な生じ方では起こらない。着用直後の船酔い感は，2・3日で消失する。体を水平方向に回転させた場合の前庭動眼反射は，メガネ着用後最初の2日間で急速に振幅が減少し，2週間から3週間たつと反射の方向が反転して，振幅は回復する。第1次視覚野の受容野は，中心視領域を除くと対側視野に限られるはずであるが，メガネ着用数週間で，対側だけでなく同側にも受容野が出現する。そのころになると，自分の手を視覚的にイメージする際も，左右反転メガネを通してみた見え方でイメージするようになる。長期間の着用を終えてメガネをはずすと，頭の動きに伴う視野動揺，動作の困難，不快感などの激しい残効に見舞われるが，そのほとんどは数時間で消失する。

Reversal of visual input has been used to investigate the mechanism of spatial cognition and adaptability since Stratton（1897） first invereted his visual field continuously. This article describes the immediate and long-term effects of reversing visual input by focusing on left-right reversal. With reversal of the visual field, normal visuomotor coordination is no longer appropriate, resulting in difficulty in movements as well as disturbance of spatial vision. The disturbance of spatial vision includes incompatibility between touch and vision, loss of spatial localization, separation of visible and tangible body, swinging of the scene, reversed depth perception in binocular stereopsis, and so on. Continuous wearing of reversing spectacles diminishes these abnormal perceptual phenomena. However, the restoration does not occur in a simple and whole fashion like reversing a negative of a photograph. Motion sickness disappears in two or three days of wearing spectacles. Vestibulo-ocular reflex to horizontal head movements becomes weak in the first two days, and its direction is reversed in two to three weeks with restoration of its amplitude. Receptive field of the primary visual cortex, which should be contralateral especially for the periphery of the visual field, becomes bilateral in a few weeks. Around then, when a wearer imagines the right hand, he/she visualizes it as if the hand were viewed through reversing spectacles. On removal of the spectacles, acute aftereffects such as swinging of the scene, difficulty in movements, and a kind of motion sickness occur, but most of them disappear in a few hours.